The present invention relates to hydraulic lash adjusting tappets of the type having a roller follower for contacting the cam shaft in an internal combustion engine valve gear. In modern overhead cam type engine valve gear, it has been desired to reduce the power consumption of the valve gear by providing roller followers on the hydraulic tappet to reduce the frictional forces created by contact of the engine cam shaft with the tappet. However, in valve gear of the overhead cam type where the tappet is the only link between the cam shaft and the valve rocker arm, i.e. where there is no push rod between the tappet and the rocker arm, space constraints have made the incorporation of roller follower tappets in existing engines quite difficult.
Where an existing valve gear of the overhead cam type having flat base tappets contacting the cam is desired to be converted to roller follower tappets, it has been found difficult to provide for maintaining proper tappet orientation and the addition of the roller follower within the length constraints established for the engine by the fixed distance between the cam shaft and the rocker arm. When converting an overhead cam engine valve gear to roller follower tappets, it is necessary to not only shorten the hydraulic lash adjusting components by an amount sufficient to provide for the incorporation of the roller follower, but it is also necessary to provide for orientation of the tappet to maintain the alignment of the roller follower with the cam. It is also necessary to maintain the supply of fluid from the engine oil flow circuit to the interior of the tappet for supplying the hydraulic lash adjusting valve. Tappets of the type having flat base frictional contact with the cam lobe may rotate freely in the tappet guide bore in the engine. In order to maintain the tappet roller oriented properly with respect to the engine cam load, registration surfaces are usually provided on the tappet for sliding engagement with a guide means provided on the engine to maintain the proper tappet orientation.
This problem of length constraints is not encountered in retrofitting engines having push rod type valve gear with roller follower tappets such as shown in FIG. 8 because the tappet may be increased in length to accommodate the roller follower and the orientation means or registration surfaces and the wide circumferential collector groove employed to fluidly connect with the engine oil circuit left intact, and the push rod shortened accordingly to compensate for the increased tappet length.